This proposal is designed to determine the role of intracellular calcium in the mechanism of insulin action. There are two organelles that appear to be of primary importance in the fine regulation of intracellular calcium, the plasma membranes and endoplasmic reticulum. Studies to date have shown that both of these organelles in the insulin target cell, the adipocyte, have specific high affinity (Ca2 ion plus Mg2 ion)-ATPases which appear to regulate Ca2 ion transport. The endoplasmic reticulum Ca2 ion transport system has been shown to be stimulated by insulin treatment of adipocytes. In contrast, the plasma membrane (Ca2 ion plus Mg2 ion-ATPase is inhibited by direct addition of the hormone to the enriched plasma membrane fraction. Further studies are designed to determine the biochemical mechanisms involved in insulin's regulation of these systems and to determine the relationship of these changes in Ca2 plus homeostasis to other known insulin-induced changes in cellular metabolism.